Industrial Health 2005, 43, 623–629 Original Article Influence of Overtime Work, Sleep Duration, and Perceived Job Characteristics on the Physical and Mental Status of Software Engineersa Mariko NISHIKITANI, Mutsuhiro NAKAO, Kanae KARITA, Kyoko NOMURA and Eiji YANO* Department of Hygiene and Public Health, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan Received January 26, 2005 and accepted August 9, 2005 Abstract: To investigate the impact of overtime work, sleep duration, and perceived job characteristics on physical and mental status, a cross-sectional study was conducted on 377 workers (average age; 28 years old) in an information-technology (IT) company, engaged in consultation, system integration solution, and data management relevant to IT system. The psychophysical outcomes of overtime work were assessed using the Hamilton Depression Scale (HDS), Profile of Mood Status (POMS), major physical symptoms, and overtime work data for the preceding three-months. Sleep duration was directly asked by a physician. A job strain index was defined as the ratio of job-demands to job- control scores evaluated using the Job Content Questionnaire (JCQ). In a univariate analysis, overtime work was significantly related with HDS scores, POMS anger-hostility scores, and the total physical symptom count in both sexes (all p<0.05), but not in multiple regression models, after controlling for sleep duration and the job strain index. Sleep duration was negatively related to the symptom count in men and to POMS tension-anxiety scores in women (both p<0.05); the job strain index was positively related to POMS anger-hostility scores in both sexes and to HDS scores and POMS tension-anxiety scores in men (all p<0.05). Although overtime work was associated with physical and mental complaints, sleep duration and the job strain index seemed to be better indicators for physical and mental distress in overloaded workers. Key words: Job strain, Overtime work, Physical and mental status, Sleep, Worker’s health examination Introduction experiencing anxiety, distress, and mental pressure in the workplace2). Overtime work tends to be longer for young- In Japan, the total number of cases of occupational and middle-aged employees, especially in large companies3). accidents and diseases has decreased since 19551). However, The JMHLW has recently established a guideline, the results of regular medical examinations showed that “Comprehensive Program for the Prevention of Health 47.3% of workers had some abnormalities in 20032). Impairment Due to Overwork (2002)”4). According to the According to a survey undertaken by the Japanese Ministry guideline4), Japanese employers are required to limit extra of Health, Labour and Welfare (JMHLW), the number of working hours to less than 45 h/month, because workers who complain mental fatigue rather than physical epidemiological studies have been shown that the risks of fatigue has been increasing, and there are many more workers cerebro- and cardio-vascular diseases increase when employees work more than 45 overtime h/month5, 6). Moreover, a Presented at the Fourth Symposium organized by the National Conference if overtime work exceeds 100 h in any month, or averages on Promotion of Occupational Health Research Priorities, November 5, 80 h/month for 2 to 6 months, employers are required to 2004, Tokyo, Japan. 4) *To whom correspondence should be addressed. have employees consult an occupational health physician . 624 M NISHIKITANI et al. There are no current guidelines for physicians when caring we excluded managers and shift-workers, and selected 377 for these workers. It is difficult to establish such guidelines individuals (304 men and 73 women) who reported their because symptoms related to overtime work are mainly working time for analysis in the study. attributed to individual lifestyle factors and greatly affected The company’s Safety and Health Committee approved by each working environment7). It is important, therefore, the study as ethical, and it was conducted with written to assess the effects of lifestyle factors and working informed consent. environment simultaneously when evaluating physical and mental status in association with overtime work. Of the lifestyle Indexes of workload factors, short sleep duration is one of the most important The following three variables were selected to measure problems among overloaded workers, because individuals workload: who do not sleep well tend to have impaired work Overtime work: This was defined as any working hours productivity and to consume more medical resources8, 9). As that exceed normal daily hours. Data about overtime work for working environment, perceived job characteristics have were obtained from employees’ computerized attendance been extensively investigated in relation to health outcomes records, and an overtime work group was defined as those like elevated blood pressure and hemoglobin A1c10, 11). who worked more than 45 h/month of overtime in any month According to NIOSH (National Institute for Occupational during the preceding three-month period, based on the Safety and Health) occupational stress model, long-working guidelines of the JMHLW4). hours, as well as lifestyle factors and working environment, Sleep duration: Information regarding three health-related were known to aggregate workers’ health status12, 13). lifestyles (drinking alcohol, smoking, and sleep duration) However, there were few studies14) comparing all these factors was obtained using a health examination check sheet, and a to assess the effect of workload on physical and mental status physician confirmed it during the interview segment of the comprehensively. The hypothesis of the present study is health examination. Sleep duration was specifically selected that the two factors of sleep duration representing lifestyle for the analysis because researchers have reported that factors and perceived job characteristics representing working insufficient sleeping hours are closely related to work environment can independently predict the physical and overload and can induce adverse health outcomes8, 9). mental status of those who are exposed to overtime work at Perceived job characteristics: These were measured using health examinations. A simple monitoring of working time the Japanese version of the Job Content Questionnaire (JCQ), may be not sufficient to screen distressed workers; to maintain which researchers have already confirmed as reliable and the physical and mental health of all workers, it may be valid15). The questionnaire consists of three scales: job necessary to monitor their life style and working environment demands, control, and social support. A job strain index in addition to their working time. was selected rather than a job demands scale during our To test the hypothesis, we examined how overtime work, analysis, because the job strain index is used more often to sleep duration, and perceived job characteristics are assess an individual’s risk of cerebro- and cardiovascular associated with the physical and mental status of young diseases6, 10, 16, 17). Individuals completed the JCQ prior to Japanese workers assigned to the same type of job. their interview with the physician. Materials and Methods Physical and mental status Subjects completed the following three questionnaires for Study setting and subjects the assessment: The survey was carried out during a mandatory periodic Hamilton Depression Scale (HDS): The 17-item version health examination in an information service company in of the HDS was used to assess the degree of depression18). Tokyo. The workers were employed in the development Because the HDS items need to be confirmed by an and management of office software and, during most of their interviewer, the HDS was completed by individuals during working time, they operated computers. their interview with the physician. Among approximately 1,000 employees, 524 individuals Profile of Mood State (POMS): The POMS was (438 men and 86 women) aged 40 yr or younger received administered to assess mood states; the reliability and validity annual examinations at the health center of the company. of the POMS has been established in a Japanese population19). The company referred individuals over 40 to an external Both tension-anxiety and anger-hostility scales were selected health examination center. Among the 524 eligible subjects, for the analysis. Industrial Health 2005, 43, 623–629 INFLUENCE OF OVERWORK ON HEALTH STATUS IN WORKERS 625 Total physical symptom count: A medical checklist about Table 1. Characteristics of age and exposure variables; 26 physical symptoms was distributed during the last week overtime work, sleep duration, and job strain index in both and the last month before the interview. Based on our sexes (values are percentages with observation numbers in parentheses) previous studies20) and on Western studies among primary care patients21), the following 12 common major medical % (n) Men (n=304)Women (n=73) symptoms were selected for the analysis: fatigue, headache, Agea insomnia, back pain, abdominal pain, joint or limb pain, <25 yr 22 (67) 41 (30) dizziness, chest pain, constipation, palpitation, nausea, and 25–30 yr 43 (130) 49 (36) shortness of breath. Symptoms once a week or more 30–35 yr 24 (74) 7 (5) ≥ frequently were defined as positive, and the total number 35 yr 11 (33) 3 (2) of positive symptoms (0–12) was used to predict impairment Overtime workb <45 h/month 65 (198) 83 (61) in physical, psychological, and social functioning20–22). 45–80 h/month 30 (91) 15 (11) 80–100 h/month 2 (6) 1 (1) Statistical methods ≥100 h/month 3 (9) 0 (0) The effects of overtime work on physical and mental status Sleep durationc were analyzed at the cut-off level of 45 overtime h/month, <5 h/night 6 (18) 8 (6) and then at two additional cutoff points of 80 and 100 5–6 h/night 24 (74) 18 (13) overtime h/month. Student’s t-test or Wilcoxon’s rank sum 6–7 h/night 46 (138) 40 (29) ≥ test was used for continuous variables, and a chi-square test 7 h/night 24 (73) 33 (24) d or Fisher’s exact test was used for categorical variables.